Basic Documentation

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Siemens Modular Heating Controller RMH760B CE1P3133en
Building Technologies 5 General functions, fundamentals 2017-09-29
The actuator running time must be matched to the type of actuator used.
This setting is important for both 3-position and DC 0…10 V actuators.
If in doubt with 3-position actuators, the setting is to be increased since otherwise the
actuator will not optimally operate in the range between 0 and 100 % stroke (also refer
to synchronization pulse in subsection 5.7.3).
It is important to also set the actuator running time with DC 0…10 V actuators. Only this
ensures correct operation of the control system.
The P-band Xp is given in K (Kelvin).
If, after a setpoint step, the control deviation equals the P-band, the valve will be
readjusted by 100 %.
With a P-band of 40 K and a setpoint change of 5 K, the valve will be readjusted by
5 / 40 = 12.5 %. Using an actuator with a running time of 150 seconds, for example, this
means that it takes the actuator 18.75 seconds to fully open or fully close.
If the P-band is increased, the controller will respond less promptly to the same control
deviation. With a P-band of 60 K, for example, the actuator will only require
12.5 seconds to travel to the fully open or fully closed position.
Increase of P-band Xp means: The control responds more slowly and there is less
tendency to oscillate.
This means:
The control action is too slow.
Decrease P-band Xp in steps of about 25 %
The control action is too fast.
Increase P-band Xp in steps of about 25 %
The integral action time Tn is indicated in seconds and amounts to about 3 × Tu (also
refer to "Setting rules" above). Tu is impacted by great filter time constants, especially
in the case of fast controlled systems.
The integral action time indicates how long it takes the controller in the event of a
constant temperature deviation to deliver the same valve travel as this would be the
case with the P-part.
For example, an integral action time of 120 seconds means that in the event of a
control deviation of 5 K in the above example (Xp = 40 K), it takes the mixing valve
120 seconds to travel 2 × 12.5 % toward the fully open or fully closed position (12.5 %
due to the P-part and 12.5 % due to the I-part).
If the integral action time is increased, the control system will respond more slowly but
becomes more stable.
5.7.3 Control signal
Since the control algorithm uses a stroke model which does not provide control beyond
0 % and 100 % respectively, the use of electrothermal actuators is no longer possible,
as this was the case with the RVL47controllers.
For 3-position control, the actuator’s current position is acquired by a stroke model. As
soon as the stroke model reaches 0 % or 100 % respectively, a synchronization signal
(continuous on pulse or continuous off pulse for 1.5 times the running time) is delivered
to the actuator, thus making certain it has reached the relevant position.
This synchronization pulse is repeated for one minute at 20-minute intervals if no
setpoint of a heating group is present.
If a position change is called for, the synchronization pulse will immediately be stopped.
Actuator running time
Note
P-band Xp
Example
Basic rule
Integral action time Tn
Electrothermal actuators
Synchronization
pulse